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TransEqns.m

TransEqns.m — Objective-C source code, 1Kb

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function PostImpact = TransEqns(Pre_Impact)
% This function relates the pre-impact state to the post-impact state.
% The eqns can be derived by using the prinicple of conservation of
% angular momentum.  The stance & swing leg angles are related by geometry
% and the two eqns for angular velocity come from: (1) conservation of 
% angular momentum (for the entire system) about the contact point, and (2)
% conservation of angular momentum about the hip (for the swing leg).  
% c.f. http://ruina.tam.cornell.edu/research/topics/...
% locomotion_and_robotics/papers/simplest_walking/...
% simplest_walking_gomes.pdf
% for complete details regarding the derivation.


theta    = Pre_Impact(1);
phi      = Pre_Impact(2);
thetadot = Pre_Impact(3);
phidot   = Pre_Impact(4);



PostImpact = [-1,  0, 0,                             0;...
              -2,  0, 0,                             0;...
               0,  0, cos(2*theta),                  0;...
               0,  0, cos(2*theta)*(1-cos(2*theta)), 0]*Pre_Impact;



end
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